Comparison of Rheological Behavior of Polyureas Based on Chain Extenders Containing p- Phenyl, m- Phenyl, and Furan Spacers

Polyurea samples with two types of hard segments have been developed, with one forming hydrogen-bonding arrays and the other forming two double hydrogen bonds separated by a spacer. The spacer is chosen to be p-phenyl, m-phenyl, and furan groups. The molecular weights are strictly controlled to be similar for the three samples. Their closely matching linear viscoelastic responses suggest compatible apparent activation energy for dissociation of hard segments from the hard domains. Nevertheless, they exhibit markedly different nonlinear elongational behavior under strong elongational flow: the degree of strain hardening follows the order p-phenyl < m-phenyl < furan. This difference reflects differences in network reconstruction: the furan-based network shows the highest ability to reconstruct after flow-induced breakup, possibly because the polar ring facilitates dissociated hydrogen bonds in finding partners, which also leads to improved strain at break at service temperature.